The present invention relates to optical communication networks generally, and more particularly to optical switching in optical communication networks.
The increase of data rates carried by optical communication networks that is experienced today makes switching operations that require optical-to-electronic and electronic-to-optical conversions of communicated information undesirable. On the other hand, all-optical switching in all-optical communication networks, particularly in applications that involve wavelength division multiplexing (WDM) and in applications that require speedup and slow-down of the communicated information, is not trivial. Thus, efficient techniques for all-optical switching that supports speedup and slow-down of communicated information in non-WDM based optical communication networks and in WDM based optical communication networks are still required.
A technique that uses a delay line together with multiplexing and modulation in order to increase a data rate carried over a single fiber optic cable is described in an article entitled xe2x80x9cMining the Optical Bandwidth for a Terabit per Secondxe2x80x9d, by Alan Eli Wiliner in IEEE Spectrum, April 1997, pp. 32-41. However, the technique described by Willner is not suitable for use with a plurality of separate fiber optic cables carrying data after the data is already modulated, and is also not suitable for use in cases where there is no synchronization between separate fiber optic cables carrying data.
Some aspects of technologies and art related to all-optical clock-recovery in optical communication networks are described in the following publications:
an article entitled xe2x80x9cPolarization Insensitive Widely Tunable All-Optical Clock Recovery Based on AM Mode-Locking of a Fiber Ring Laserxe2x80x9d, by Wang et al in IEEE Photonics Technology Letters, Vol. 12, No. 2, February 2000, pp. 211-213;
an article entitled xe2x80x9cUltra-High-Speed PLL-Type Clock Recovery Circuit Based on All-Optical Gain Modulation in Traveling-Wave Laser Diode Amplifierxe2x80x9d, by Kawanishi et al in Journal of Lightwave Technology, Vol. 11, No. 12, December 1993, pp. 2123-2129; and
an article entitled xe2x80x9cPrescaled 6.3 GHz clock recovery from 50 GBit/s TDM optical signal with 50 GHz PLL using four-wave mixing in a traveling-wave laser diode optical amplifierxe2x80x9d, by Kamatani et al in Electronics Letters, Vol. 30, No. 10, May 12, 1994, pp. 807-809.
Some aspects of technologies and art related to delay line techniques are described in the following publications:
an article entitled xe2x80x9cVariable optical delay line with diffraction-limited autoalignmentxe2x80x9d by Klovekorn et al in Applied Optics, Vol. 37, No. 10, Apr. 1, 1998, pp. 1903-1904;
an article entitled xe2x80x9cPicosecond-Accuracy All-Optical Bit Phase Sensing Using a Nonlinear Optical Loop Mirrorxe2x80x9d, by Hall et al in IEEE Photonics Technology Letters, Vol. 7, No. 8, August 1995, pp. 935-937; and
an article entitled xe2x80x9cAn Ultrafast Variable Optical Delay Techniquexe2x80x9d, by Hall et al in IEEE Photonics Technology Letters, Vol. 12, No. 2, February 2000, pp. 208-210.
Some aspects of technologies and art related to all-optical demultiplexing techniques are described in the following publications:
an article entitled xe2x80x9cCompact 40 Gbit/s optical demultiplexer using a GaInAsP optical amplifierxe2x80x9d, by Ellis et al in Electronics Letters, Vol. 29, No. 24, Nov. 25, 1993, pp. 2115-2116;
an article entitled xe2x80x9cBit-Rate Flexible All-Optical Demultiplexing Using a Nonlinear Optical Loop Mirrorxe2x80x9d, by Patrick et al in Electronics Letters, Vol. 29, No. 8, Apr. 15, 1993, pp. 702-703; and
an article entitled xe2x80x9cAll-Optical High Speed Demultiplexing with a Semiconductor Laser Amplifier in a loop Mirror Configurationxe2x80x9d, by Eiselt et al in Electronics Letters, Vol. 29, No. 13, Jun. 24, 1993, pp. 1167-1168.
Some aspects of technologies and art related to WDM based and non-WDM based optical communication networks and to optical switching techniques and elements associated therewith are described in the following publications:
The Communications Handbook, CRC Press and IEEE Press, 1997, Editor-in-Chief Jerry D. Gibson, Chapter 65, pp. 883-890;
an article entitled xe2x80x9cOptical switching promises cure for telecommunications logjamxe2x80x9d, by Jeff Hecht in Laser Focus World, September 1998, pp. 69-72;
a technology brief entitled xe2x80x9cLucent Upgrades Wavestar to 320-Channel, 800-Gb/s Transmissionxe2x80x9d, in Photonics Spectra, June 2000, pp. 46;
an article entitled xe2x80x9cDesign and Cost Performance of the Multistage WDM-PON Access Networksxe2x80x9d, by Maier et al in Journal of Lightwave Technology, Vol. 18, No.2, February 2000, pp. 125-143;
an article entitled xe2x80x9cAll-optical networks need optical switchesxe2x80x9d, by Jeff Hecht in Laser Focus World, May 2000, pp. 189-196;
an article entitled xe2x80x9cRecord Data Transmission Rate Reported at ECOC 96xe2x80x9d, by Paul Mortensen in Laser Focus World, November 1996, pp. 40-42;
an article entitled xe2x80x9cMultiple Wavelengths Exploit Fiber Capacityxe2x80x9d, by Eric J. Lerner in Laser Focus World, July 1997, pp. 119-125;
an article entitled xe2x80x9cAdvances in Dense WDM Push Diode-Laser Designxe2x80x9d, by Diana Zankowsky in Laser Focus World, August 1997, pp. 167-172;
an article entitled xe2x80x9cMultistage Amplifier Provides Gain Across 80 nmxe2x80x9d, by Kristin Lewotesky in Laser Focus World, September 1997, pp. 22-24;
an article entitled xe2x80x9cWDM Local Area Networksxe2x80x9d, by Kazovsky et al in IEEE LTS, May 1992, pp. 8-15;
an article entitled xe2x80x9cOptical Switches Ease Bandwidth Crunchxe2x80x9d, by Rien Flipse in EuroPhotonics, August/September 1998, pp. 44-45;
an article entitled xe2x80x9cSpeed Demons: Is xe2x80x9cFaster Better and Cheaper?xe2x80x9d, by Stephanie A. Weiss in Photonics Spectra, February 1999, pp. 96-102;
an article entitled xe2x80x9cWavelength Lockers Keeps Lasers in Linexe2x80x9d, by Ed Miskovic in Photonics Spectra, February 1999, pp. 104-110;
an article entitled xe2x80x9cOptical switches pursue crossconnect marketsxe2x80x9d, by Hassaun Jones-Bay in Laser Focus World, May 1998, pp. 153-162;
a conference review entitled xe2x80x9cOptical amplifiers revolutionize communicationsxe2x80x9d, by Gary T. Forrest in Laser Focus World, September 1998, pp. 28-32;
an article entitled xe2x80x9cCombining gratings and filters reduces WDM channel spacingxe2x80x9d, by Pan et al in Optoelectronics World, September 1998, pp. S11-S17;
an article entitled xe2x80x9cDemand triggers advances in dense WDM componentsxe2x80x9d, by Raymond Nering in Optoelectronics World, September 1998, pp. S5-S8;
an article entitled xe2x80x9cOptical Networks Seek Reconfigurable Add/Drop Optionsxe2x80x9d, by Hector E. Escobar in Photonics Spectra, December 1998, pp. 163-167;
an article entitled xe2x80x9cUltrafast Optical Switch Unveiledxe2x80x9d, by Michael D. Wheeler in Photonics Spectra, December 1998, pp. 42;
an article entitled xe2x80x9cData express Gigabit junction with the next-generation Internetxe2x80x9d, by Collins et al in IEEE Spectrum, February 1999, pp. 18-25;
an article entitled xe2x80x9cDesigning Broadband Fiber Optic Communication Systemsxe2x80x9d, by Juan F. Lam in Communication Systems Design magazine, February 1999, pp. 1-4 at http://www.csdmag.com;
an article entitled xe2x80x9cTerabit/second-transmission demonstrations make a splash at OFC ""96xe2x80x9d, in Laser Focus World, April 1996, pp. 13;
an article entitled xe2x80x9cMultigigabit Networks: The Challengexe2x80x9d, by Rolland et al in IEEE LTS, May 1992, pp. 16-26;
an article entitled xe2x80x9cDirect Detection Lightwave Systems: Why Pay More?xe2x80x9d, by Green et al in IEEE LCS, November 1990, pp. 36-49;
an article entitled xe2x80x9cPhotonics in Switchingxe2x80x9d, by H. Scott Hinton in IEEE LTS, August 1992, pp. 26-35;
an article entitled xe2x80x9cAdvanced Technology for Fiber Optic Subscriber Systemsxe2x80x9d, by Toba et al in IEEE LTS, November 1992, pp. 12-18;
an article entitled xe2x80x9cFiber amplifiers expand network capacitiesxe2x80x9d, by Eric J. Lerner in Laser Focus World, August 1997, pp. 85-96;
an article entitled xe2x80x9cTechnologies for Local-Access Fiberingxe2x80x9d, by Yukou Mochida in IEEE Communications Magazine, February 1994, pp. 64-73;
an article entitled xe2x80x9cWavelength Assignment in Multihop Lightwave Networksxe2x80x9d, by Ganz et al in IEEE Transactions on Communications, Vol. 42, No. 7, July 1994, pp. 2460-2469;
an article entitled xe2x80x9cWavelength-Division Switching Technology in Photonic Switching Systemsxe2x80x9d, by Suzuki et al in IEEE International Conference on Communications ICC ""90, pp. 1125-1129;
an article entitled xe2x80x9cBranch-Exchange Sequences for Reconfiguration of Lightwave Networksxe2x80x9d, by Labourdette et al in IEEE Transactions on Communications, Vol. 42, No. 10, October 1994, pp. 2822-2832; and
an article entitled xe2x80x9cUse of Delegated Tuning and Forwarding in Wavelength Division Multiple Access Networksxe2x80x9d, by Auerbach et al in IEEE Transactions on Communications, Vol. 43, No. 1, January 1995, pp. 52-63.
Additionally, asynchronous time-division switching is described in The Communications Handbook, CRC Press and IEEE Press, 1997, Editor-in-Chief Jerry D. Gibson, Chapter 51, pp. 686-700. Multiple access methods for communications networks are described in The Communications Handbook, CRC Press and IEEE Press, 1997, Editor-in-Chief Jerry D. Gibson, Chapter 46, pp. 622-649
U.S. Pat. No. 5,170,273 to Nishio describes a cross-talk reducing optical switching system which receives electrical digital signals at its input terminal.
U.S. Pat. No. 5,191,457 to Yamazaki describes a WDM optical communication network in which optical beams are modulated by channel discrimination signals of different frequencies.
U.S. Pat. No. 5,194,977 to Nishio describes a wavelength division switching system with reduced optical components using optical switches.
U.S. Pat. No. 5,557,439 to Alexander et al. describes wavelength division multiplexed optical communication systems configured for expansion with additional optical signal channels.
U.S. Pat. No. 5,680,490 to Cohen et al. describes a comb splitting system which demultiplexes and/or multiplexes a plurality of optical signal channels at various wavelengths.
U.S. Pat. No. 5,712,932 to Alexander et al. describes reconfigurable wavelength division multiplexed systems which include configurable optical routing systems.
U.S. Pat. Nos. 5,724,167 and 5,739,935 to Sabella describe an optical cross-connect node architecture that interfaces plural optical fiber input and output links, each link containing plural wavelength channels.
U.S. Pat. No. 5,457,687 to Newman describes reactive congestion control in an ATM network where the network is formed by the interconnection of nodes each including a forward path for transfer of information from source to destination through the network and a return path for returning congestion control signals.
Copending U.S. patent application Ser. No. 09/126,378 filed on Jul. 30, 1998 and assigned to the assignee of the present application describes improvements in communication performance of an optical communication system that communicates data via N different channel wavelengths using WDM.
Copending U.S. patent application Ser. No. 09/389,345 filed on Sep. 3, 1999 and assigned to the assignee of the present application describes a network control system that may be embodied in various elements of a communication network that communicates optical signals multiplexed by WDM. The network control system may limit a number of channel wavelengths actually used for communicating optical signals to an end node, and control and modify data rates carried over channel wavelengths multiplexed by WDM.
The disclosures of all references mentioned above and throughout the present specification are hereby incorporated herein by reference.
The present invention seeks to improve optical switching and routing in all-optical communication networks, and particularly in wavelength division multiplexing (WDM) based optical communication networks.
In the present invention, an optical switching apparatus that is associated with a communication switch of an all-optical communication network enables speedup or slow-down of optical communication substantially without using optical-to-electronic and electronic-to-optical conversions of communicated information. In order to speedup or slow-down optical communication the optical switching apparatus combines or separates respectively series of optical signal samples representing the information by selectively using optical time-division multiplexing (OTDM) techniques and WDM techniques.
There is thus provided in accordance with a preferred embodiment of the present invention an optical switching method for switching n series of upstream optical signal samples to a destination route, each series of upstream optical signal samples in the n series of upstream optical signal samples being carried over a channel wavelength xcexi at a data rate DRi, where n is an integer and i is an index running from 1 to n, the method including the steps of optically converting the n series of upstream optical signal samples into a combined series of upstream optical signal samples having the upstream optical signal samples carried over a channel wavelength xcexD at a combined data rate DRc which is greater than any separate DRi, the channel wavelength xcexD being useful for carrying optical signal samples to the destination route, and routing the combined series of upstream optical signal samples to the destination route. Preferably, DRc is one of the following: equal to xcexa3i=1, . . . ,nDRI, and similar to xcexa3i=1, . . . ,n DRi.
The optically converting step preferably includes converting any of the xcexi that differ from xcexD to xcexD thereby forming a group of n series of upstream optical signal samples having the upstream optical signal samples carried over xcexD, and combining the n series of upstream optical signal samples in the group so as to provide the combined series of upstream optical signal samples.
Preferably, the upstream optical signal samples in each of the n series of upstream optical signal samples are spaced by a time spacing T, and the combining step includes recovering a clock signal CLKi for each series of upstream optical signal samples in the group, generating time delays of at least a fraction of T between every two series of upstream optical signal samples in the group so as to create a group of n sequentially delayed series of upstream optical signal samples in which a delay between every two series of upstream optical signal samples is at least a fraction of T, and multiplexing the n sequentially delayed series of upstream optical signal samples in the group so as to provide the combined series of upstream optical signal samples.
The multiplexing step preferably includes multiplexing the n sequentially delayed series of upstream optical signal samples in the group by using synchronous time-division multiplexing when DR1=, . . . ,=DRn, and multiplexing the n sequentially delayed series of upstream optical signal samples in the group by using asynchronous time-division multiplexing when at least some of the data rates DR1, . . . ,DRn are different from each other.
Preferably, the destination route includes at least one of the following: a destination fiber optic cable capable of carrying optical signal samples at the combined data rate DRc, a wireless communication route, a waveguide, a transmission line, an interface to a destination optical transceiver, and an interface to a destination optical communication system operating at the combined data rate DRc.
In a case where the n series of upstream optical signal samples are coded in a line code other than a return-to-zero (RZ) line code, the method also includes converting the n series of upstream optical signal samples coded in the line code other than an RZ line code into n series of RZ coded upstream optical signal samples prior to the optically converting step, and converting the combined series of upstream optical signal samples into a combined series of upstream optical signal samples coded in the line code other than an RZ line code after the optically converting step.
Preferably, the method also includes the step of selecting the channel wavelength xcexD prior to the optically converting step.
The method may also preferably include, prior to the optically converting step, the steps of selecting the n series of upstream optical signal samples from groups of k1, . . . ,km series of upstream optical signal samples that are respectively carried over m separate fiber optic cables in a wavelength division multiplexed form over channel wavelengths {xcexiijj} at data rates {DRiijj} respectively, where k1, . . . ,km are integers greater than one, m is an integer greater than or equal to one, ii is an index running from 1 to m, and jj is an index running from 1 to kj where j is an index running from 1 to m, and dropping the n series of upstream optical signal samples from those of the m separate fiber optic cables that carry the n series of upstream optical signal samples.
Preferably, the dropping step includes demultiplexing at least those of the groups of k1, . . . ,km series of upstream optical signal samples that include the n series of upstream optical signal samples so as to provide LK demultiplexed series of upstream optical signal samples, where LK is an integer greater than one, and selecting each of the n series of upstream optical signal samples from the LK demultiplexed series of upstream optical signal samples.
There is also provided in accordance with a preferred embodiment of the present invention an optical switching method for switching a series of downstream optical signal samples which is carried over a channel wavelength xcexT at a data rate DRT to nn routes, where nn is an integer greater than one, the method including the steps of optically converting the series of downstream optical signal samples into nn series of downstream optical signal samples having the downstream optical signal samples carried over channel wavelengths xcex1, . . . ,xcexnnxe2x88x921, xcexT at data rates DRT1, . . . ,DRTnn respectively, where xcex1#xcexT, . . . ,xcexnnxe2x88x921#T and each of DRT1, . . . , DRTnn is less than DRT, and routing the nn series of downstream optical signal samples to the nn routes respectively.
Preferably, the optically converting step includes separating the series of downstream optical signal samples so as to provide a group of nn series of downstream optical signal samples having the optical signal samples in each series of downstream optical signal samples in the group carried over xcexT at a respective one of the data rates DRT1, . . . , DRTnn, and converting xcexT of all except one of the series of downstream optical signal samples in the group into the channel wavelengths xcex1, . . . ,xcexnnxe2x88x921 so as to provide the nn series of downstream optical signal samples having the downstream optical signal samples carried over the channel wavelengths xcex1, . . . ,xcexnnxe2x88x921, xcexT at the respective data rates DRT1, . . . ,DRTnn.
The separating step preferably includes using synchronous time-division demultiplexing for separating the series of downstream optical signal samples so as to provide the group of nn series of downstream optical signal samples in which DRT1=, . . . ,=DRTnn, and using asynchronous time-division demultiplexing for separating the series of downstream optical signal samples so as to provide the group of nn series of downstream optical signal samples in which at least some of the data rates DRT1, . . . ,DRTn are different from each other.
Additionally, the method also includes the step of selecting the channel wavelengths xcex1, . . . ,xcexnnxe2x88x921 prior to the optically converting step.
Further in accordance with a preferred embodiment of the present invention there is also provided an optical communication signal useful for communication to at least one of a node server and an end node of an optical communication network, the optical communication signal including a series of optical signal samples having the optical signal samples carried over a channel wavelength xcexD at a data rate DRc, the series of optical signal samples being produced by optically converting n series of optical signal samples in which the optical signal samples are respectively carried over channel wavelengths xcex1, . . .,xcexn at data rates DR1, . . . ,DRn, where n is an integer and DRc is greater than any one of DR1, . . . ,DRn.
In accordance with yet another preferred embodiment of the present invention there is also provided an optical switching apparatus for switching n series of upstream optical signal samples to a destination route, each series of upstream optical signal samples in the n series of upstream optical signal samples being carried over a channel wavelength xcexi at a data rate DRi, where n is an integer and i is an index running from 1 to n, the optical switching apparatus including an upstream optical converter unit operative to convert the n series of upstream optical signal samples into a combined series of upstream optical signal samples having the upstream optical signal samples carried over a channel wavelength xcexD at a combined data rate DRc which is greater than any separate DRi, the channel wavelength xcexD being useful for carrying optical signal samples to the destination route, and a upstream router operatively associated with the upstream optical converter unit and operative to route the combined series of upstream optical signal samples to the destination route.
Additionally, the optical switching apparatus may also preferably include a controller operatively associated with the upstream optical converter unit and operative to perform at least one of the following: to determine the number n of series of upstream optical signal samples, and to select the channel wavelength xcexD.
Preferably, the upstream optical converter unit includes an upstream wavelength converter unit operative to convert any of the xcexi that differ from xcexD to xcexD thereby forming a group of n series of upstream optical signal samples having the upstream optical signal samples carried over xcexD, and a combiner operatively associated with the upstream wavelength converter unit and operative to combine the n series of upstream optical signal samples in the group so as to provide the combined series of upstream optical signal samples.
The upstream optical signal samples in each of the n series of upstream optical signal samples are preferably spaced by a time spacing T, and the combiner preferably includes a clock-recovery unit operative to recover a clock signal CLKi for each series of optical signal samples in the group, an optical delay mechanism operatively associated with the clock-recovery unit and operative to generate time delays of at least a fraction of T between every two series of upstream optical signal samples in the group so as to create a group of n sequentially delayed series of upstream optical signal samples in which a delay between every two series of upstream optical signal samples is at least a fraction of T, and a multiplexer operatively associated with the optical delay mechanism and operative to multiplex the n sequentially delayed series of upstream optical signal samples in the group so as to provide the combined series of upstream optical signal samples.
Preferably, the multiplexer includes at least one of the following: a synchronous time-division multiplexer, and an asynchronous time-division multiplexer.
Additionally, the apparatus may also preferably include, for use in a case where the n series of upstream optical signal samples are coded in a line code other than an RZ line code, a line code converter unit operatively associated with the upstream optical converter unit and the upstream router and operative to convert the n series of upstream optical signal samples coded in the line code other than an RZ line code into n series of RZ coded upstream optical signal samples prior to conversion of the n series of upstream optical signal samples into the combined series of upstream optical signal samples in the upstream optical converter unit, and to convert the combined series of upstream optical signal samples into a combined series of upstream optical signal samples coded in the line code other than an RZ line code after conversion of the n series of upstream optical signal samples into the combined series of upstream optical signal samples in the upstream optical converter unit.
Preferably, the controller, or an additional controller that may be included in the optical switching apparatus and operatively associated with the upstream optical converter unit, is operative to select the n series of upstream optical signal samples from groups of k1, . . . ,km series of upstream optical signal samples that are respectively carried over m separate fiber optic cables in a wavelength division multiplexed form over channel wavelengths {xcexiijj} at data rates {DRiijj} respectively, where k1, . . . ,km, are integers greater than one, m is an integer greater than or equal to one, ii is an index running from 1 to m, and jj is an index running from 1 to kj where j is an index running from 1 to m, and a multiplexing/demultiplexing unit operatively associated with the upstream optical converter unit and the controller and operative to drop the n series of upstream optical signal samples selected by the controller from those of the m separate fiber optic cables that carry the n series of upstream optical signal samples. The multiplexing/demultiplexing unit preferably includes at least one add drop multiplexer (ADM).
The optical switching apparatus may preferably be embodied in a communication switch of a communication network that includes a node server and a plurality of end nodes and may preferably be operatively associated with the node server and the plurality of end nodes.
There is also provided in accordance with still another preferred embodiment of the present invention an optical switching apparatus for switching a series of downstream optical signal samples which is carried over a channel wavelength xcexT at a data rate DRT to nn routes, where nn is an integer greater than one, the optical switching apparatus including a downstream optical converter unit operative to optically convert the series of downstream optical signal samples into nn series of downstream optical signal samples having the downstream optical signal samples carried over channel wavelengths xcex1, . . . ,xcexnnxe2x88x921,xcexT at data rates DRT1, . . . ,DRTnn respectively, where xcex1#xcexT, . . . ,xcexnnxe2x88x921#xcexT and each of DRT1, . . . , DRTnn is less than DRT, and a downstream router operatively associated with the downstream optical converter unit and operative to route the nn series of downstream optical signal samples to the nn routes respectively.
Preferably, the downstream optical converter unit includes a demultiplexer operative to separate the series of downstream optical signal samples so as to provide a group of nn series of downstream optical signal samples having the optical signal samples in each series of downstream optical signal samples in the group carried over xcexT at a respective one of the data rates DRT1, . . . , DRTnn, and a downstream wavelength converter unit operatively associated with the demultiplexer and operative to convert xcexT of all except one of the series of downstream optical signal samples in the group into the channel wavelengths xcex1, . . . ,xcexnnxe2x88x921, so as to provide the nn series of downstream optical signal samples having the downstream optical signal samples carried over the channel wavelengths xcex1, . . . ,xcexnnxe2x88x921,xcexT at the respective data rates DRT1, . . . ,DRTnn.
The optical switching apparatus may preferably be embodied in a communication switch of a communication network that includes a node server and a plurality of end nodes and may preferably be operatively associated with the node server and the plurality of end nodes.